Why do we call shorter EM wavelengths rays and longer ones waves?

[Archosaur]

I just noticed that we tend to call EM wavelengths shorter than visible light "rays" while we call we call those that are longer "waves". Why is that? Did we ever think that "rays" and "waves" were physically different?

 

[Rajini]

Ray is the name given to the beam of light. Light is just the wave and always travel with c in vacuum.

 

[pallidin]

I think there is a tendency for higher EM wavelengths to disperse less, more of a straight line beam if you will.

 

[AJ Bentley]

It's just history.

Originally, the wave nature of light wasn't known.
Before the 18th century, light was thought of as rays simply because you could see 'rays' of sunlight etc.

The wave nature of light was becoming apparent around the same time as radio waves began to be observed. It was sometime later that the two were connected.